. >>> president obama landed in johannesburg 45 minutes ago. and he is one of nearly 100 heads of state attending. they will also be speaking. tina krauss on how the world will pause to remember mandela. >> reporter: south africa's national soccer stadium will be the center of the world tuesday as dozens of leaders from around the globe gather to remember nelson mandela. >> and that is exactly what he did. and that's what he does, brings people together. >> reporter: president obama will be one of the featured speakers. while the president and mandela met only once in 2005, they kept in touch by telephone since the president first took office in 2008. former presidents george w. bush, bill clinton, and jimmy carter will also attend the massive memorial. this stadium holds nearly 100,000 people, but many more want to be here. thousands will watch from surrounding streets on big stream. before tuesday's public memorial, family and close friends pay their respects in private. mandela's eldest grandson and leader of the clan joined the crowd outsid